Effect of the as-built microstructure on the martensite to austenite transformation in a 18Ni maraging steel after laser-based powder bed fusion

Author(s)

Conde, F. F. ^[1] ; Avila, J. A. ^{[2, 3]} ; Oliveira, J. P. ^[4] ; Schell, N. ^[5] ; Oliveira, M. F. ^[1] ; Escobar, J. D. ^[6]

Affiliation

^[1] Univ Sao Paulo, Dept Mat Engn, Av Joao Dagnone 1100, BR-13563120 Sao Carlos - Brazil

^[2] Sao Paulo State Univ UNESP, Campus Sao Joao da Boa Vista, BR-13876750 Sao Joao Da Boa Vista, SP - Brazil

^[3] Univ Autonoma Occidente UAO, Calle 25, Via Cali Puerto Tejada 115-85 Km 2, Cali, Valle Del Cauca - Colombia

^[4] NOVA Univ Lisbon, NOVA Sch Sci & Technol, Dept Mech & Ind Engn, UNIDEMI, P-2829516 Caparica - Portugal

^[5] Helmholtz Zentrum Hereon, Inst Mat Phys, Max Planck Str 1, D-21502 Geesthacht - Germany

^[6] Univ Sao Paulo, Met & Mat Engn Dept, 10 Av Prof Mello Moraes 2463, BR-05508030 Sao Paulo, SP - Brazil

• Document type: Journal article
• Source: ADDITIVE MANUFACTURING; v. 46, OCT 2021.
• Web of Science Citations: 0

Abstract

During laser-based powder bed fusion, the non-equilibrium solidification conditions promote local elemental segregation, leading to a characteristic microstructure composed of cellular walls. These walls can display either low carbon BCC martensite or FCC retained austenite crystal structures, thus affecting the subsequent isochronal or isothermal martensite to austenite phase transformation mechanisms. In the present study, the effect of the non-homogeneous as-built microstructure on the martensite-to-austenite reversion phenomena was studied for a 18Ni maraging steel fabricated by laser-based powder bed fusion. In-situ synchrotron X-ray diffraction was used to retrieve the austenite volume fraction and lattice parameter evolution during the physical simulation of continuous heating cycles to the austenitic field; and during isothermal tempering cycles throughout the intercritical tempered martensite + austenite (alpha' + gamma) field. The as-built microstructure resulted in the expansion of the inter-critical alpha' + gamma field during very slow heating rates. This was associated to the synergic effects of compositional segregations (anticipating reversion) and pre-existing retained austenite (delaying solubilization). During conventional inter-critical tempering, the as-built microstructure did not fundamentally alter the austenite reversion kinetics, resulting in similar high temperature microstructures at the end of the isothermal stage relative to the solution treated state. (AU)

• FAPESP's process: 17/17697-5 - Mechanical and microstructural assessment of additive manufacturing parts made up of 18%Ni Maraging 300 steel towards aeronautic application.
• Grantee: Julian Arnaldo Avila Diaz
• Support Opportunities: Regular Research Grants
• FAPESP's process: 19/00691-0 - Microstructural assessment of additive manufacturing parts towards aeronautic application
• Grantee: Julian Arnaldo Avila Diaz
• Support Opportunities: Regular Research Grants